The present invention relates to hydraulic control systems for controlling the operation of fluid-operated units, particularly but not solely, support props of mine workings.
Mining apparatus employing roof supports of various kinds usually have control valves or devices used to connect pressure fluid feed and return lines to the props and supporting rams. Such control devices are usually manually-operated although some apparatus does utilize remote control. When the support props are extended to cause the roof engaging caps or the like carried thereby to contact the roof, it is vitally important to ensure the props are correctly set with the maximum pressure bearing on the roof before subsequent operations are carried out. This is, however, not always achieved. Visual inspection of the props cannot assist in this regard, since although the roof caps may contact the roof, this is not necessarily indicative that the lower working chambers of the props have reached the desired setting pressure. Consequently, there is a danger that the control devices may break connection between the fluid supply and the props prematurely before the correct setting pressure is reached.
A general object of the present invention is to provide an improved control system which will overcome this problem.